  <!DOCTYPE html>
  <html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
      * {
        padding: 0;
        margin: 0;
		box-sizing: border-box;
      }

.container {
  overflow: hidden;
  border: 3px solid black;
}
      .parter {
        /* 用padding-bottom撑开box, 然后用margin-bottom将边界打回*/
        padding-bottom: 9999px;
        margin-bottom: -9999px;
      }

      .middle{
        float: left;
        background-color: red;
        width:100%;
      }
      .inner {
        margin: 0 200px;
        
      }
      .left {
        float: left;
        width: 200px;
        background-color: yellow;
        margin-left: -100%
      }
      .right {
        float: left;
        width: 200px;
        background-color: green;
        margin-left: -200px;

      }
    </style>
  </head>
  <body>
    <div class="container">
      <!-- 把中间部分前在前面，优先渲染 -->
      <div class="parter middle">
        <div class="inner">中</div>
      </div>
      <div class="parter left" style="border-right:1px solid black">左 <p>另一行</p><p>另一行</p><p>另一行</p>
        </div>
      <div class="parter right" style="border-left:1px solid black">右</div>
  </div>
  </body>
  </html>